Joint apparatuses have been widely applied to animals, human bodies, mechanical apparatuses, or various industrial goods.
In general, the functions of joints are to provide: 1) a motion in a preset direction and a positional restoration, 2) a formation of one structure by one part and the other part in a combined state, and 3) a capability of being kept in one structure when no external force is applied, and separated when an external force over a particular strength is applied, and (4) a recombination to perform the original function once it is separated.
Although the joint apparatus should include the above functions, there is a limit that a general joint apparatus includes the above function (Korean Patent No. 1132806, Korean Patent Publication No. 2012-0020727)